Recently, systems have been developed by which a secret decryption key is in the hands of several trustees, so that each trustee holds a guaranteed piece of the key, while he cannot predict the full key. Examples of such systems include Micali's Fair Cryptosystems and the Clipper Chip.
We want to develop such a system in a public key setting so that the secret key that is guaranteed to be shared among some trustees is the secret decryption key corresponding to a given public encryption key. The inventive system does not work by having an initial entity who (1) computes a public-secret key pair, and (2) divides the secret key among various trustees in a proper way. Indeed, whether or not such entity blows itself up after doing so (e.g., as suggested by Desmet), the doubt exists that leakage of the secret decryption key may have occurred, either maliciously or by accident.